Sammanfattning: The aim of this thesis was to study maternal and infant effects of delayed cord clamping (?180 seconds, DCC) compared to early (?10 seconds, ECC) in a randomised controlled trial. Practice and guidelines regarding when to clamp the cord vary globally, and different meta-analyses have shown contradictory conclusions on benefits and disadvantages of DCC and ECC.The study population consisted of 382 term infants born after normal pregnancies and randomised to DCC or ECC after birth. The primary objective was iron stores and iron deficiency at 4 months of age, but the thesis was designed to investigate a wide range of suggested effects associated with cord clamping.Paper I showed that DCC was associated with improved iron stores at 4 months (45% higher ferritin) and that the incidence of iron deficiency was reduced from 5.7% to 0.6%. Neonatal anaemia at 2-3 days was less frequent in the DCC group, 1.2% vs. 6.3%. There were no differences between the groups in respiratory symptoms, polycythaemia, or hyperbilirubinaemia.In paper II we demonstrated that DCC versus ECC was not associated with higher risk for maternal post partum haemorrhage and rendered a comparable ratio of valid umbilical artery blood gas samples.In paper III, the Ages and Stages Questionnaire was used to assess neurodevelopment at 4 months. The total scores did not differ, but the DCC group had a higher score in the problem-solving domain and a lower score in the personal-social domain. Immunoglobulin G level was 0.7 g/L higher in the DCC group at 2–3 days, but did not differ at 4 months. Symptoms of infection up to 4 months were comparable between groups.Finally, in paper IV, iron stores and neurodevelopment were similar between groups at 12 months. Gender specific outcome on neurodevelopment at 12 months was discovered, implying positive effects from DCC on boys and negative on girls.We conclude that delaying umbilical cord clamping for 180 seconds is safe and associated with a significantly reduced risk for iron deficiency at 4 months, which may have neurodevelopmental effects at a later age.